1. Field of the Invention
This invention relates to a dry, non-clumping herbicidal composition together with a method for making the composition.
More particularly, the present invention relates to a method for making an ammonium glyphosate herbicide by directly reacting ammonia gas with glyphosate acid. The reaction product dissolves readily and completely in water and can be used to prepare highly-loaded, adjuvant-containing dry glyphosate compositions.
2. Description of the Related Art
N-phosphonomethylglycine [HOOCCH.sub.2 NH CH.sub.2 PO(OH).sub.2 ], which is commonly referred to as glyphosate acid or simply glyphosate, is well known in the art as a highly effective herbicide. It is also known that glyphosate, an organic acid, has relatively low solubility in water. Thus, glyphosate is typically formulated as a water-soluble salt, particularly as the mono-isopropylamine (IPA) salt to kill or control weeds or plants. Glyphosate is sold commercially as an aqueous concentrate in the form of its IPA salt by Monsanto Company of St. Louis, Mo. (U.S.A.) under the registered trademark Roundup.RTM..
Various salts of glyphosate, methods for preparing salts of glyphosate, formulations of glyphosate and methods of use for killing and controlling weeds and plants are disclosed in U.S. Pat. Nos. 3,799,758 and 4,405,531 issued to John E. Franz on Mar. 26, 1974 and Sep. 20, 1983 respectively. Other U.S. Patents which disclose salts of glyphosate include U.S. Pat. No. 4,315,765 issued to George B. Large on Feb. 16, 1982, U.S. Pat. No. 4,507,250 issued to Izak Bakel on Mar. 26, 1985, U.S. Pat. No. 4,397,676 issued to Izak Bakel on Aug. 9, 1983, U.S. Pat. No. 4,481,026 issued to Michael P. Prisbylla on Nov. 6, 1984 and U.S. Pat. No. 4,140,513 issued to Erhard J. Prill on Feb. 20, 1979. All of the foregoing patents, in their entireties, are herein incorporated by reference.
Roundup.RTM. brand herbicide is sold as a water-soluble liquid concentrate. However, efforts have recently been made in the art to develop a water-soluble dry/solid glyphosate formulation which has the equivalent efficacy of Roundup.RTM..
Conventional reasons underlying these efforts have been desired cost savings in connection with the packaging, shipment and storage of a solid formulation versus a liquid. As can be appreciated, aqueous concentrates include a significant amount of solvent that adds to the size and weight of packaging containers and increases costs associated with post-manufacture delivery of the product to market.
A less readily apparent benefit also resides in the advantage of making a water-soluble, dry glyphosate. Namely, a granular formulation is believed to provide superior handling characteristics (i.e. controlled spillage) and is expected to be substantially lighter and less awkward to transport (and often hand carry) thereby making the product better suited for use in remote geographic locations.
Making a granular glyphosate formulation, however, entails overcoming inherent disadvantages relating principally to the increased production cost and comparative complexity of compounding a solid product from a combination of gaseous and solid reactants rather than making a product in solution from the same reactants.
Several methods of making a solid water-soluble glyphosate salt-containing composition are known. For example, in U.S. Pat. No. 5,047,079 which issued on Sep. 10, 1991 to Djafar, there is disclosed a method for preparing a phytotoxic composition comprising admixing isopropylamine with a molten surfactant to form a matrix, the surfactant being a solid at ambient temperatures.
In U.S. Pat. No. 5,070,197 which issued on Dec. 3, 1991 to Chin, et. al. an extrusion method is disclosed in which a Bronsted acid, N-phosphonomethyl glycine for example, is intimately admixed with sodium hydroxide in an extruder to produce a granular extrudate having a residual moisture content of no greater than 10%. Another method involving the production of a dry sodium glyphosate composition, albeit not involving extrusion, is disclosed in PCT application Publication No. WO 87/04595.
In U.S. Pat. No. 5,266,553 which issued on Nov. 30, 1993 to Champion, et. al. there is disclosed a method for preparing a dry, water-soluble salt of bentazon or of an herbicide containing a carboxylic acid functionality which involves repeated treatments of the salt with a neutralizing base selected from the group consisting of ammonia, an alkylamine, a hydroxyalkylamine, an alkaline salt of an alkali metal and combinations thereof.
In French Patent Publication No. 2.692.439 which was filed on May 19, 1993 and is assigned to Productos Osa SACIFIA, there is generally described a phytotoxic preparation comprising the monoammonium salt of N-phosphonomethylglycine as a powder or granule in combination with a wetting agent, surfactant and/or a pulverulent additive. As exemplified in the reference, the monoammonium salt is derived from reacting glyphosate acid with ammonium carbonate.
U.S. Pat. No. 5,324,708 which issued on Jun. 28, 1994 to Moreno, et. al. discloses a composition and related methods for preparing and using a non-hygroscopic monoammonium glyphosate salt such as the mono-isopropylammonium salt of N-(phosphono-methyl)-glycine and the mono-isopropylammonium salt of (3-amino-3-carboxypropyl)-methane phosphonic acid in dry powder form [sic].
In PCT application Publication No. WO 94/10844, published on May 26, 1994, a dry glyphosate composition is disclosed in which N-phosphonomethyl glycine is admixed with, inter alia, an inorganic or organic, non-caustic base material such as diammonium phosphate or a basic guanidine salt such as guanidinium acetate.
EPO application Publication No. 0 394 211 which was published on Oct. 24, 1990, discloses an invention comprising a dry pesticidal composition and related methods of use and production. More particularly, the invention relates to the enhanced solubility of the composition as achieved by the addition of an effective amount of an organosilicone block copolymer or a fluorocarbon wetting agent.
In EPO application Publication No. WO 90/07275 which was published on Jul. 12, 1990, there is disclosed an invention by which granular, water-soluble glyphosate compositions are made as by admixing, pan granulation, drying, spraying and extrusion.
In PCT application Publication No. WO 92/12637, which was published on Aug. 6, 1992, there is disclosed an invention relating to a dry, water soluble glyphosate including a composition comprising substantially nonreacted glyphosate, an acid acceptor such as sodium acetate and a liquid or solid surfactant.
All of the foregoing patents and publications are herein incorporated by reference.
The art indicates that considerable effort has been directed toward formulating compositions and related methods for making and using dry glyphosates. However, none of the above-identified references disclose a direct and practical method for producing a dry, water-dispersible, water-soluble and appreciably non-hygroscopic ammonium glyphosate composition which is capable of absorbing/adsorbing an exceptionally high level of adjuvants by reacting solid N-phosphonomethylglycine with relatively inexpensive and plentiful ammonia gas.
Thus, a need unsatisfied by known technology exists within the art for the present invention which accomplishes these and other objectives.